Most cardiac pacemakers today (including implantable cardioverter/defibrillators with pacing capability) are microprocessor-based systems in which software run by the microprocessor commands the generation of pacing outputs, with various timers being used to alert the microprocessor as to when to pace. Such microprocessor-based systems exhibit great flexibility, as compared with a pacemaker implemented with dedicated hardware, since the operation of the device can be changed simply by reprogramming the microprocessor. Controlling the operation of a pacemaker totally with a microprocessor-based system, however, also has some disadvantages. If the microprocessor continually executes instructions during the cardiac cycle in order to process and respond to timing and sensing events, a large amount of battery power is consumed. Also, making pacing decisions with software inevitably introduces some variability into the timing of the paces, commonly referred to as “pacing jitter.”